1. Field of the Disclosure
The present disclosure relates generally to a multi-subscription device, and more particularly, to a method for reducing a conflict during a cell search procedure in a multi-subscription device.
2. Description of the Related Art
There is an increasing demand for devices that can support multiple subscriptions, thereby supporting simultaneous wireless, e.g., cellular, access with different networks, such as different public land mobile networks (PLMNs) and/or networks operated by different carriers and/or different network operators. In order to support multiple subscriptions, devices, such as mobile terminals, may include multiple subscriber identity modules (SIMs). In this regard, devices that include two SIMS are often referred to as dual SIM devices. However, devices may include any number of SIMs for supporting three, four, five or more subscriptions.
In some wireless networks, a user equipment (UE) may have multiple subscriptions to one or more networks (e.g., by employing multiple SIM cards or otherwise). Such a UE may include, but is not limited to, a dual-SIM, dual standby (DSDS) device.
In DSDS devices, the user may establish a call, such as a voice call, data call, data session, text messaging session, or any other data transfer session, via one of two subscriptions. Because most DSDS devices contain a single radio resource, such as a transceiver, where a first subscription has established an ongoing call with a first subscription network, the UE must tune the transceiver to a second subscription to receive necessary paging signals and to transmit, for example, message acknowledgement signals and/or measurement indication signals. Therefore, while the first subscription continues an ongoing call, the transceiver may periodically tune away from the first subscription to the second subscription to receive such necessary paging and/or control information.
In some situations, such as where a UE reselects a new cell for one of its subscription services, it must undertake a cell search procedure. A cell search procedure typically includes a series of synchronization stages by which the mobile device determines parameters that are necessary to demodulate a downlink and to transmit uplink symbols with correct timing. In multi-radio access technology systems, a cell search procedure is performed for a plurality of radio access technologies. For example, the multi-radio access technology system may include global system for mobile communications (GSM), wideband code division multiple access (WCDMA) and long term evolution (LTE). A mobile device then undertakes a cell search for any radio access technology (RAT) it can operate and more in time division duplex (TDD) systems where uplink and downlink switching is frequent.
Further, a cell search procedure is divided across multiple layers and upper layers will not be able to know about conflicts at lower layers. A search time for one frequency may vary from technology to technology and is also time dependent upon the procedures at the lower layer.
In any DSDS device, where radio frequency (RF) resources are shared across many SIMs when a cell search procedure is initiated on one SIM, another SIM is required to perform periodic procedures like reading paging/measurements at the same time. During the scanning of frequencies, the RF may be taken away by the other SIM, resulting in an interruption, thereby causing a performance reduction. If multiple frequencies are being scanned during a cell search procedure, interruptions from another SIM may cause the procedure to provide incomplete results, thus leading to a failure.
FIG. 1 is a flow diagram 100 illustrating periodic RF interruptions during cell search, according to the related art.
Referring to FIG. 1, the flow diagram 100 includes an upper layer 102, a lower layer 104 and another SIM 106. Initially, the resources are assigned to a different SIM and the different SIM may perform any procedure, such as, but not limited to, a call, such as a voice call, a data call, a data session, text messaging session, any other data transfer session, and the like. The other SIM 106 which is idle requires RF resources to perform periodic paging searches and other related tasks. If the resources are within the other SIM 106, the upper layer 102 transmits a cell search request to the lower layer 104 in step 108. Upon receiving the cell search request, the lower layer 104 receives periodic RF interruptions from the other SIM 106 in step 110. Upon receiving period RF interruptions, the lower layer 104 transmits a cell search failure to the upper layer 102 in step 112. The process of transmitting a cell search request and a cell search failure continues between the upper layer 102 and the lower 104 in steps 114, 116, and 118 while the resources are within the other SIM 106.
FIG. 2 is a diagram 200 illustrating signaling information during cell search interruption of a first SIM (SIM1), according to the related art.
Referring to FIG. 2, initially, RF resources are assigned to the SIM1 while a second SIM (SIM2) is in an idle state. During an active state, the SIM1 initiates cell searching in step 202. During a cell search of SIM1, SIM2 receives paging and measurement information in step 204 and, thus, the resources assigned to SIM1 are shared with SIM2. After a certain period of time, a discontinuous reception (DRX) cycle of SIM2 starts in step 206 and, thus, the resources remain with SIM2. Since the resources are with SIM2, no conflict arises in step 208 and SIM1 continues to wait for the resources for performing a cell search.
After a certain time, a timer expires for SIM1 as SIM1 does not receive the resources and, thus, the cell search of SIM1 is interrupted in step 210. After a certain time period, SIM2 receives paging and management information in step 212, and continues accessing the resources. After a certain time interval, SIM1 attempts to access the resources for a cell search and identifies that the resources are with SIM2 in step 214. Thus, SIM1 continues to wait for the certain time period to receive the resources. Upon the expiration of the timer, SIM1 identifies that the resources are unavailable since they are with SIM2, the cell search of SIM1 is interrupted in step 216, and SIM2 receives paging and management information in step 218.
In view of the foregoing, there is a need for a system and method to reduce conflict during a cell search procedure in multi-subscription devices, such as DSDS devices.